Health challenges that lead to subclinical or clinical diseases can increase treatment costs, reduce performance and affect animal welfare. These impacts can be reduced by starting treatment early. Since behaviour is known to be affected by the health status of an animal, an early diagnosis by monitoring changes in behaviour is a possibility. The objective of this thesis was to quantify the changes in behaviour that take place as a consequence of health challenges and to asses them for their suitability to be used for the early detection of (sub) clinical disease. The behaviours looked at were: feeding; drinking; activity; and posture. In two experiments an acute health challenge was used, in the form of either a vaccination or a lipopolysaccharide bolus. These acute challenges, due to their transient nature, did not manifest as substantial changes in behaviour. A gastro-intestinal parasite (Ostertagia ostertagi) was used as a chronic challenge in three experiments. This health challenge affected several aspects of the behaviours measured. Due to its prolonged nature these effects increased over time, but were reversed after the challenge had been removed. The challenge also showed a dose dependency, demonstrating a threshold, rather than a gradient, when affecting behaviour for different levels of parasitic infection. From the overall results it was concluded that activity, posture and in some cases feeding behaviour, were affected by the parasitic (O. ostertagi) health challenge. From these, activity and posture were found to have the greatest magnitude of change and to be the most consistently affected across experiments. These behavioural changes, however, started at the same time as a rise in faecal egg counts and pepsinogen levels. Nonetheless, due to the magnitude of the behavioural changes, behaviour could still be used as an indicator of health status, predominantly in animals that receive little visual monitoring.